New details emerged Tuesday about the Boston Marathon bombing suspects as the surviving brother’s medical condition marginally improved and two of his alleged victims were buried, including an 8-year-old boy.

Tamerlan Tsarnaev, the 26-year-old suspect who died following a police shootout last week, purchased two reloadable mortar kits from a Seabrook, N.H. store on Feb. 6., according to a company official. Consumer-grade fireworks contain a limited amount of explosives, but the 48 pyrotechnic shells Tsarnaev obtained would have been enough to yield some black powder, Phantom Fireworks vice president William Weimer said in an interview from the company's Ohio headquarters.

Tsarnaev asked a question that “90 percent of the males who walk into a fireworks store ask,” said Weimer.

“’What’s the biggest and loudest thing you have?’” Tsarnaev asked, said Weimer, who has talked to the store employee who sold Tsarnaev the fireworks.

Tsarnaev paid $199.99 in cash and walked out with his two “Lock and Load” fireworks kits, Weimer said, consulting store records.

Investigators have not publicly identified the material used in the two improvised explosive devices that killed three and wounded more than 260 in two April 15 bombings near the marathon’s finish line. An FBI affidavit released this week said the bombs were made of “low-grade explosives” packed into pressure cookers along with “metallic BBs and nails.”

The same FBI affidavit also reported that investigators had found a “large pyrotechnic” at the University of Massachusetts Dartmouth dorm room in which Tsarnaev’s younger brother, Dzhokhar, lived.

Officials on Tuesday upgraded Dzhokhar Tsarnaev’s condition to fair at Beth Israel Deaconess Medical Center, where the 19-year-old is being treated for what the FBI described as “apparent gunshot wounds to his head, neck, legs and hand” suffered either during a gun battle with police in suburban Watertown early Friday or later that night when he was discovered hiding in a boat in a Watertown backyard.

Tsarneav faces federal charges of using a weapon of mass destruction and malicious destruction of property with an explosive, both of which can lead to the death penalty or a life sentence.

Tsarnaev’s federal public defender has asked that the trial judge appoint two defense attorneys with expertise in death penalty cases, citing the complexity of the charges facing Tsarnaev. On Monday, a transcript showed that Tsarnaev was read his Miranda rights, notifying him that he had the right to remain silent and to retain an attorney. But the Boston Globe and other media outlets, citing unnamed law enforcement sources, reported Tuesday that Tsarnaev had made incriminating statements on Sunday.

Tsarnaev also likely will face state charges, including murder for the shooting death of Massachusetts Institute of Technology police officer Sean Collier. The 27-year-old Collier, who investigators say was gunned down while he sat in his car in Cambridge on Thursday night, was buried following a private funeral service Tuesday.

A private service was also held for 8-year-old Martin Richard, who died in the April 15 explosion. “This has been the most difficult week of our lives,” the Richard family said in a brief prepared statement.

The marathon casualty count continued to climb, reaching 264 as of Tuesday, according to Boston Public Health Commission spokeswoman Katinka Podmaniczky. Some of these victims have been showing up with conditions like persistent hearing loss and ringing in the ears.

Among Boston-area medical facilities, Massachusetts General Hospital was still treating six marathon patients Tuesday, with one in serious condition. Brigham and Women’s Hospital was treating 10 marathon patients, two of them amputees.

Under a plan unveiled late Tuesday afternoon, called One Fund Boston, these victims will be able to apply for compensation from a pot of privately raised money that totals $20 million so far.

“It’s not a lot of money, when you look at the nature of these injuries,” fund administrator Kenneth Feinberg, who oversaw a much larger fund for 9/11 terrorism victims, said at a news conference. “It will not make these people whole.”

Slowly coming into focus, according to investigators and those briefed by them, is a picture of the two Tsarnaev brothers, ethnic Chechens, and their allegedly growing radicalization.

The law firm representing Katherine Russell, Tamerlan Tsarnaev’s wife, said Tuesday that their client is “doing everything she can to assist with the investigation.”

Russell married Tamerlan in June 2010 and the couple had a daughter, but neither she nor her family had any knowledge of his plans, the attorney said.

“The reports of involvement by her husband and brother-in-law came as an absolute shock to them all,” said the statement issued by the law firm of Amato DeLuca. “As a mother, a sister, a daughter, a wife, Katie deeply mourns the pain and loss to innocent victims – students, law enforcement, families and our community.”

The developing picture includes, as well, hints of missed opportunities for U.S. counterterror specialists. The latter theme has been particularly resonant among congressional Republicans, who turned up the heat Tuesday on alleged FBI shortcomings, recalling how similar lapses preceded the Sept. 11, 2001, terrorist attacks.

“This whole system of the right hand not talking to the left hand, pre-9/11 mentality seems to be rearing its head here,” said Sen. Lindsey Graham, R-S.C.

One problem occurred when Tamerlan Tsarnaev traveled outside of the United States. In her Senate testimony, Napolitano acknowledged that “there was a mismatch” between the spelling of the name on Tsarnaev’s airline ticket and on his identity papers. As a result, her department knew that Tsarnaev had left the country, but the FBI, which previously had questioned Tsarnaev at the request of Russian security services, did not.

“The system pinged when he was leaving the United States,” Napolitano said. “By the time he returned, all investigations had been – the matter had been closed.”

Two Senate hearings, including a closed session before the Senate intelligence committee, were followed early Tuesday evening by a briefing available to all members of the House of Representatives by Napolitano, FBI Director Robert Mueller and a member of the National Counterterrorism Center.

Maine Republican Sen. Susan Collins said following the intelligence panel briefing that she was “very concerned” about an apparent lack of information sharing, even within a single agency, while some lawmakers said the briefings were of limited value.

“Nothing you haven’t read in the newspaper,” said Rep. James Moran, D-Va., shaking his head.

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